WIP: Abstract entities

[AmaranthineCodices]

I want to abstract entities away from Roblox instances. You will still be able to attach components to instances with CollectionService tags, but the entity will no longer be a Roblox instance. It will be an opaque identifier (either a userdata or just an auto-incremented number) that has no fundamental behavior.

This will mean RECS will ship a blessed component with it: InstanceReference. InstanceReference components are attached to entities with CollectionService tags. Currently, an entity with the components DeathBrick and Sparkler looks like:

• Instance (entity)
  • DeathBrick component
  • Sparkler component

After this change, the entity will instead look like this:

• (entity)
  • InstanceReference component (referencing the instance)
  • DeathBrick component
  • Sparkler component

When the RECS core starts, it will scan for all instances with CollectionService tags. It will then create abstract entities for them with an InstanceReference component referencing the instance, along with all other applicable components (depending on the CollectionService tags on the instance).